The present invention pertains generally to molding of composite materials including fibers and plastics and, more particularly, to molding of structural and acoustical panels which include glass fibers and thermosetting resins.
Composite material panels are used in many different applications, including automobiles, airplanes, housing and building construction. The properties sought in such panels are strength, rigidity, sound absorption, and heat and moisture resistance. One application of such panels which has been especially challenging is automobile headliners and other automotive interior panels. Many different types of laminates and laminated composites have been tested and produced for use in automobiles. Some headliners have a core of fiberglass fibers and a polyester resin. Others have been manufactured from a core of open cell polyurethane foam impregnated with a thermosetting resin, and with a reinforcing layer of fiberglass. This type of construction is inefficient in mass production, and has low acoustical attenuation which is particularly undesirable for automobile headliners.
Other approaches have been to form a laminate of fiber reinforcing mat, such as a glass fiber mat on a fibrous core, and a second reinforcing mat on the opposite side. The exposed surfaces of the reinforcing mat are then coated with a resin and an outer cover stock applied. This laminate is then formed to a desired shape under heat and pressure, i.e., compression molding. Although this type of structure has somewhat improved acoustical characteristics, additional sound dampening is desired, particularly for luxury automobiles.
In the prior art, the fibrous layers of the laminates consist of fibers of relatively large and uniform denier or size. This parameter is critical to sound attenuation properties, and fibers of finer or smaller denier are required to achieve greater sound absorption. However, fine denier fibers in the range of 1.2 or less lack the resiliency required for retention of thermoformed shapes. Although resiliency can be achieved by impregnating the fibers with a resin, it is very difficult to impart an even distribution of resin into a fibrous batt containing fine denier fibers. In the prior art, extensive impregnation of the fibrous layers was not required due to the presence of the stiff reinforcing layers. Hence, given these trade-offs, a truly superior acoustical dampening headliner of sufficient strength could not be produced.
Although layers containing fiberglass have the desirable characteristics of strength and some sound attenuation, they have the undesirable traits of reflecting sound when made very hard or dense. Fiberglass, particularly in woven mat form, is also difficult to handle and is a known skin irritant. Because the production of headliners and similar panels using fiberglass is most commonly done manually, this is a significant problem which has not been addressed. Alternative fibers, natural and synthetic, have not been developed to be both cost effective and have strength comparable to glass.
The present invention overcomes these and other disadvantages of the prior art, by providing a composite material laminated structure which has all of the desired physical properties, and an improved method of manufacture. In accordance with one aspect of the invention, there is provided a laminated structure having a core of polymeric fibers, a thermosetting resin impregnated into the core, and individual chopped fibers randomly applied to opposite sides of the core layer. A decorative layer is applied to an exterior side of the laminate, and an impervious film and finish scrim is applied to the opposite side of the core. The polymeric fibers of the core are bonded together by a thermoplastic binder system. A preferred method of bonding the fibers together is by a bicomponent fiber, in which an outer layer of fibers is a low melt temperature polymer, and an inner core layer of fibers is a polymer with a relatively higher melt temperature.
In accordance with another aspect of the invention, there is provided a laminate structure with enhanced sound absorption and structural properties having a central core having opposite sides and made of a combination of intertwined polyester fibers having differing deniers in an approximate range of 0.1 to 100, the combined fibers arranged with the core to form a layer of fibers of relatively small denier adjacent to a layer of fibers of relatively large denier, a resin applied to the core, structural fibers randomly attached to the opposite sides of the core by contact with the resin, at least some of the structural fibers being intertwined with the polyester fibers of the core, a low melt polymer web over the structural fibers on one of the opposite sides of the core, and a face cloth over the low melt polymer web, an impervious polymer film over the structural fibers on an opposite side of the core, and a scrim layer over the impervious polymer film.
And in accordance with another aspect of the invention there is provided a method of manufacturing a laminate structure which can be molded into a relatively rigid structure and which is effective at absorbing sound, the method including the steps of applying a thermoset resin to the fibrous core, providing a polymer film which has a melting temperature less than a melting temperature of the fibrous core adjacent to the fibrous core, putting a plurality of reinforcing non-woven fiber strands into contact with the polymer film and a first side of the fibrous core, positioning a fibrous core containing a plurality of intertwined polyester fibers of differing denier with a thermoset resin applied to the fibrous core in contact with the plurality of reinforcing non-woven fiber strands, putting a plurality of reinforcing non-woven fiber strands into contact with a second side of the fibrous core generally opposite to the first side, applying a polymer web over the fiber strands applied to the second side of the fibrous core, and applying a cover stock to the polymer web.
These and other aspects of the invention are herein described in particularized detail with reference to the accompanying Figures.